This is one of the first four or five I did -- but I still don't know if I believe in Gaia.

We're very complicated animals, we humans. Lots and lots of busy little cells all busily and mindlessly doing what they have to, just to keep us humans going. Our cells don't know about us: we know all about our cells, but our cells can never know about us.

Some animals aren't made of cells. School-kids are usually taught to refer to the bacteria and the blue-green algae as unicellular animals. After all, says orthodoxy, these things have a membrane round the outside, and lots of works inside, rather like one of our cells, so why not regard each animal as a single cell?

These days, some biologists prefer to call them acellular, without cells, for while the things aren't divided up inside by membranes, they're still divided. And as there are no cells, they must be acellular. But whether the parts are properly separated or not, they all do their own thing, keep the whole organism alive, and they never know about the organism that they make up.

Higher up the evolutionary ladder, we find the eucaryotes, things with their cells divided up, with membranes neatly wrapping up organelles such as the chloroplasts, mitochondria, and ribosomes, and so on. These parts all work mindlessly to maintain a larger organism of which they're part, but which they'll never know about.

These eucaryotes are interesting because some people think that the organelles inside them are really other cells that have been taken on board, given a home, and put to work. A sort of cellular All Nations Club, which might be just a bit too strong on cellular miscegenation for some people.

It seems that these cells nestling up together aren't just different species, they're probably even from different phyla. But these mixed foreigners don't know much about each other, and they certainly aren't aware of the higher order cell that they make, so we can at least hope that it's all right for them to mix.

Just in case, though, we'd better not tell that man from the RSL. You see, our cells are all eucaryotic, so our cells are all these peculiar mixed-up things too. Alf Garnett would flip if he thought his innards were all made up of cohabiting foreigners. Yuchhh!

I'm delighted with the idea that my multicultural cells are all independently doing their thing, unconsciously controlling each other in some way so that I can type these words, waddle off to the ABC, and blow air up my throat while contorting my face so as to make odd noises that other people will then understand. If Old Alf is listening, I'll bet he's contorting his face and making odd noises right now, too.

One of my favourite animals, unless they're plants, or are they fungi, I never can remember, is the slime mould. A slime mould is made up of eucaryotic cells, full of organelles, but these cells wander off, like so many ants at a picnic, to gather food, commune with nature or whatever, quite independently.

There they are, these cells, generally at peace with the world, when suddenly they all start secreting a chemical, a messenger chemical that says: "Let's get together!". So suddenly, they all gather, form an organism, and generally behave like any other multicellular organism. They form what we call a fruiting body.

And yet I'm almost sure that the slime mould cells are quite unconscious of what they're doing, and quite unconscious of the fruiting body that they become.

Just now, I compared the slime mould cells with ants, but I could also have compared them with bees, or some other social insect. Have you ever stopped to wonder if the ant's nest has some degree of self-consciousness, in the way that the larger vertebrates do?

Think about those ants that form nests and bridges by linking their bodies together: aren't they just like the cells of the slime mould? Could there be something about a colony of ants that makes it more than just the sum of its parts? In the fashionable parlance of the New Biology, should we look beyond Reductionism to Holism? Douglas Hofstadter certainly thinks so.

In his remarkable book, "Godel, Escher, Bach: an Eternal Golden Braid", published some ten years ago, Hofstadter introduces a character called Ant Hillary, a decidedly self-conscious ant-hill, and explores this question at far more length than I have time for here today. You'll have to read the book.

By the time he's finished, though, you'll be convinced that an ant-nest can be an organism, just like a slime mould, but one step higher. Think about it: the nest is made up of ants, unconscious of the higher organism that they make, but that's not all.

Each ant is made of cells, all unconscious of the higher organism that they make, and each cell is made up of organelles, all unconscious of the higher organism that they make.

You could keep on going, down through the molecules, the atoms, the particles, the quarks, the sub-quarks, and so on, but let's agree on the organelle as the base-order organism. The acellular organism would also be a first-order organism: after all, we think that some of them became the organelles.

The eucaryotic cell is a second-order organism, ants, slime mould fruiting bodies and humans are all third-order, and a nest of ants, or bees, or termites, is about as close as we get to a fourth-order organism. Maybe such things are still evolving.

The interesting thing is that each of these organisms, no matter what its order, behaves much like any other organism. So there's no logical or biological reason why there shouldn't be even higher-order organisms. The components would never be aware that they were part of a greater whole, but I suspect that if there were a fourth-order organism, of which we were not part, we would be aware of it, just as we know about the social insects.

And that, long-windedly, brings me to Gaia. James Lovelock proposed this idea about twenty years ago, in an article that I recall reading in "New Scientist". In its essence, this suggested that all living things form a self-sustaining and self-regulating system: the whole biosphere of the planet Earth is a single entity, said Lovelock.

As any good self-confident reductionist would, I told myself that he was nuts, and turned to the next article in that week's issue. Now, I'm not quite so sure about that: maybe there was something in it, after all.

The real problem with the Gaia hypothesis is that the loony green fringe has adopted Gaia as a sort of God-away-from-God, who'll one day come crashing down from that Great Ecology in the Sky, smiting the unecological, and tormenting the environmental sinners with plagues of nameless abominations, genetically designed to scald and viper through them, munching on their entrails, and generally leaving them as socially undesirable messes that you wouldn't want to invite round for a few drinks and a pleasant dinner.

Well, Lovelock did go asking for it a bit, what with giving his putative super-organism the name of a Greek Earth Goddess. That really got the neo-pseudo-theologists going. Gave them all a field day, you might say.

Yet whether he went asking for it or not, Lovelock didn't deserve dear old Isaac Asimov, who introduced his version of Gaia in the fifth volume of the Foundation trilogy or thereabouts. In my callow youth, I thought Isaac was a pretty hot writer, but in my callow middle age, I wish he'd stopped at the third part of the trilogy.

The good doctor's Gaia is a planet-full of people in telepathic contact with each other, where even the rocks get into the act and send small gritty thoughts to each other...and everybody else!

The bits of Asimov's Gaia might function as some kind of super-organism, but they'll never pass my test for super-organisms: the different elements of this Gaia all know about each other, and so Asimov's Gaia is a false one. While the elements of a super-system might be convinced of their own free will, I think it would destroy the system to have them aware of their own parts in that system.

Can you imagine what would happen if your cells all knew about each other, and about you? How long would it be before your Red Cells led a revolution? How long would it take for your Islets of Langerhans to secede? Or until your aqueous humour developed a sense of humour, and fed false images to the optic system?

Lovelock's Gaia hypothesis originally was based on the assumption that there had to be a willful, deliberate Gaia maintaining the status quo on the Earth, keeping conditions right for living things.

It was, he said, unlikely that the conditions necessary for life would have obtained long enough to let life flourish all this time. So something had to be doing something about our environment, or we wouldn't be here to talk about it. There had to be a Causal Agent.

Looking at it the other way, unless the improbable happened somewhere, there wouldn't be any place at all in the Universe where life could develop to intelligence at the third order level, or any other level, for that matter. Possibly we just drew the long straw, so that our system survived long enough for us to evolve.

We're here, so whatever unlikely things were needed to bring that about, they happened. End of theological argument. But even if you don't have to assume that there's some kind of fourth, or even fifth-order being, it's fun to contemplate what that being is like.

I mean, if we were all part of a fourth-order organism, would it be aware that we were self-aware? Or would we just be specialised sub-units in Gaia's view, a bit like nerves in a human? Not really self-aware, not as Gaia understands the term, but carrying definite elements of information.

Again, how would we let Gaia know that we're here and starting to suss out that Gaia is there? And how could we prove for ourselves that Gaia really exists? Would we disappear into a chronosynclastic infundibulum if we got into contact or dialogue with Gaia?

To get some idea of what Gaia might be like, let's look at the only fourth-order organisms that we can find, the termites, the ants, and the bees. They may be poor examples of the full potential of a fourth-order organism, but they're the best that we've got.

They're all quite ruthless about individual organisms, killing off the sick, just as we destroy cells in our body that are diseased. So if Gaia does exist, and we're part of it, then we should find our population under some similar kind of control. We shouldn't be able to have a population explosion.

Or would we? Don't we suffer from cancers, where, all of a sudden, one group of cells or another starts to multiply furiously? Could humans be a cancerous growth in Gaia's terms, rocketing out of control, threatening to destroy the whole intricate web that is Gaia? We seem to have overcome all of the natural controls that keep any given population of sub-units in check.

Well maybe not quite all of the controls: AIDS might have sprung up as a control factor, aiming to bring the cancerous human growth back under control. How's that for a wild theory? We get rid of smallpox, and Gaia substitutes AIDS to keep us in check?

Hmmmm, I seem to be getting onto the same wave-length as those who see AIDS as the wrath of God. Still, at least my speculation is based on the idea that maybe there's some useful purpose for it all, other than the chastisement of those somebody calls wicked.

Of course, all of this assumes some sort of rather deliberate and self-willed Gaia, directing its attention to curing imbalances, the sort of Gaia that the greenies look for, the one that will suddenly produce black flowers to warm up the earth, or whatever. And not even Lovelock argues for that sort of Gaia any more, so we'll have to explain AIDS some other way.

And I can't say that I really believe that there's any such thing as a Gaia that incorporates us and every other living thing: all of the other fourth-order examples that we can identify seem to be made up of genetically similar individuals of one species, so a multi-species Gaia seems just that little bit improbable.

Still, whether an all-human Gaia exists or not, it's an amusing and instructive thing to ponder over and speculate about. Are the electronic media, for example, the Gaian equivalent of hormones in the human body? If the signals reach other inhabited planets, would that make them the equivalent of pheromones? You can go on forever.

The beautiful part, though, is that, speculate as you will, we can never know if we're part of some higher-order grouping. With due respect to Dr. Asimov, it seems to be against the rules. But who wrote the rules, that's what I'd like to know. Maybe, just maybe, it was Gaia.